Impossible to tell without a meter. Most homes are wired with a 60amp or 100amp (max) Panel. Checking how many amps are being drawn off a main hot wire should do the trick.
Actually... a house...
It depends entirely on your type of monitor and power supply, but you can figure on the average of 100 watts per amp (that's a generalization of course). If you have for instance, a 350 watt power...
A 100 amp service will supply your electrical current needs UP TO 100 amps.
When doing load calculations on a 100 amp panel it can only be loaded up to 80 amps.